Functional gastrointestinal pain syndromes may be referred to the esophagus, stomach, small bowel, colon, and/or rectum. Presentation is often
complex and symptoms may overlap, but generally include complaints of
nausea, vomiting, bloating, altered bowel patterns, and most commonly
chronic intermittent pain. Broadly defined, these disorders include non-
cardiac chest pain (NCCP), nonulcer dyspepsia (NUD), and the irritable
bowel syndrome (IBS). Together, these functional pain syndromes constitute the most frequent reasons for consultation with gastroenterologists.
Abdominal pain is the defining characteristic and the least understood
manifestation of these syndromes. The goal of this chapter is to evaluate the
mechanisms responsible for pain complaints in gastrointestinal pain syndromes and to determine if each represents different manifestations of a
common altered physiology, or whether each reflects different symptom and
pathophysiologic profiles. The biopsychosocial aspects of chronic pain in
functional bowel patients are also reviewed to emphasize the complexity of
providing care for the patient with chronic visceral pain.

The Physiologic Basis of Chronic Pain

Merskey and
Bogduk ( 1994) defined pain as the sensory and emotional
sequelia resulting from insult to tissue. However, most patients with functional bowel disorders experience pain chronically or intermittently without evidence of organic lesions. Chronic pain may, therefore, be defined

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